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Lt. Gov. David Dewhurst formally launched his campaign for the U.S. Senate on Tuesday, an expected move that puts the Houston multimillionaire into a crowded Republican primary of people vying to succeed Sen. Kay Bailey Hutchison.

Dewhurst filed paperwork with the Federal Election Commission and sent a three-minute video to about 500 supporters, campaign manager Jim Bognet told The Associated Press.

In the video, Dewhurst pledged to be "unapologetically conservative and as serious as the problems we're currently facing."

He said he's going to sign a pledge to "cut, cap and balance" federal spending and government. The video will be posted for wider distribution on Wednesday and Dewhurst has scheduled a campaign tour around the state in September.

As lieutenant governor, Dewhurst is the presiding officer over the Republican-controlled state Senate. Dewhurst plans to keep his job while campaigning for the Senate, Bognet said.

Dewhurst, 65, had been widely expected to join the Republican primary field. Other candidates include former Texas Solicitor General Ted Cruz, former Dallas Mayor Tom Leppert and former Texas Railroad Commissioner Elizabeth Ames Jones.

All hope to fill the seat held by Hutchison, a Republican who is not running for re-election in 2012.

Dewhurst is expected to be willing to spend some of his personal fortune, which he made in oil and gas, on his campaign.

"I'm running for the United States Senate to help take our country back," Dewhurst said in the video. "Our nation has gotten off track. Washington spends money we don't have on programs we don't need, while 14 million Americans remain out of work."

Dewhurst grew up in Houston and attended the University of Arizona, where he played basketball for two years and studied history. After graduation, he became an officer in the U.S. Air Force and then went to work for the CIA for two years in Bolivia, where he learned to speak Spanish.

Dewhurst entered the public sector in 1999 when he won the commissioner's post at the General Land Office, which manages state lands to create education revenue and oversees the public school fund.

After one term as land commissioner, Dewhurst in 2002 beat veteran politician John Sharp to win the lieutenant governor's post, often considered the state's most powerful statewide elected seat because the officeholder controls the flow of legislation in the Senate and appoints senators to legislative committees.